You need ST-Link V2 Programmer

First download the ST link Utility from the following ST Micro site:
https://www.st.com/en/development-tools/stsw-link004.html

Register yourself and download the zip file.

Unzip and install it and launch.
Now, insert the ST-Link Programmer to the USB port.

From top menu, Select:  ST-Link -> Firmware Upgrade 

Click on Device Connect button

If there is an error message, re insert the ST-Link Programmer to the USB Port.

You can see the current firmware version and available new version.
Just click on Upgrade firmware (Yes  >>>)button.